MANUFACTURING METHOD OF SEAMLESS STEEL PIPE OF HARDLY MACHINABLE MATERIAL

• Main Authors: GOTO JOGO, OZAKI SEIJI, KATSUMURA TATSURO, SHIRASAKI KIMITO
• Format: Patent
• Language: English; Japanese
• Published: 18.08.2016
• Subjects: MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVINGMATERIAL; PERFORMING OPERATIONS; PUNCHING METAL; ROLLING OF METAL; TRANSPORTING

PROBLEM TO BE SOLVED: To provide a manufacturing method of a seamless steel pipe, the method that reduces an internal surface flaw occurring in a hollow element tube without decreasing a plug life even when boring and rolling a round billet of a hardly machinable material with internal defects such as center porosity therein.SOLUTION: A seamless steel pipe has a tapered cylindrical protrusion where a taper angle which increases the outer diameter as it goes to the rear end in the axial direction is θ, an axial length is A2, and a distal surface is formed of a spherical surface shape of a curvature radius r. A plug is used which has a shape shown in Fig. 1 and with an overall length A, a maximum outer diameter D, the taper angle θof the protrusion, the axial length A2 and the curvature radius rof the distal surface satisfying the following expressions (1) to (3). The expression (1) is 0.110≤r/D≤0.182, the expression (2) is 0.023≤A2/A≤0.093, and the expression (3) is 5°≤θ≤20°.SELECTED DRAWING: Figure 1 【課題】中心ポロシティー等の内部欠陥が存在する難加工性材料の丸ビレットを穿孔圧延した場合にもプラグ寿命を低下することなく、かつ、中空素管に発生する内面疵を低減する継目無鋼管の製造方法を提供する。【解決手段】先端部に外径が軸方向後端に向かうに従って増大するテーパ角度θ＊、軸方向長さＡ２、先端面が曲率半径ｒ＊の球面状で形成されるテーパ円柱状の突起を有し、全長Ａ、最大外径Ｄ、前記突起のテーパ角度θ＊、軸方向長さＡ２、および先端面の曲率半径ｒ＊が下記（１）ないし（３）式を満足する図１に示す形状のプラグを用いる。０．１１０≦ｒ＊／Ｄ≦０．１８２...（１）０．０２３≦Ａ２／Ａ≦０．０９３...（２）５°≦θ＊≦２０°...（３）【選択図】図１